1. Field of the Invention
The present invention relates to a nonaqueous-electrolyte battery.
2. Description of the Related Art
In recent years, with the development of portable electronic apparatus, high performance batteries have been desired. A lithium ion battery, in which a carbon material is used in a negative electrode and lithium cobaltate in the form of lamellar composite oxide is used in a positive electrode, has been put in practical use as a nonaqueous-electrolyte battery having a high operating voltage and a high energy density. However, since lithium cobaltate is poor in natural resources and thus is expensive, lithium-containing manganese composite oxide or lithium nickelate has been proposed as a substitute. Such a composite oxide is an positive active material for so-called 4V lithium secondary battery which operates at around 4 V on the average.
On the other hand, since the development of ICIs operating at a voltage as low as not higher than 3 V is under way, or from the standpoint of battery safety, it is expected that the demand for 3V nonaqueous electrolyte secondary battery will be increasing. However, as an positive active material for 3V nonaqueous electrolyte secondary battery, there are generally Known only LiMnO2 and V2O5. Even these substances are much disadvantageous in discharge capacity or cycle life and find extremely limited application such as memory backup.
Further, it has been recently reported that oxyhydroxide of nickel can be used as an positive active material for 3V nonaqueous electrolyte secondary battery (Lecture No. 3A06 at the 64th Conference of The Electrochemical Society of Japan). According to this report, oxyhydroxide of nickel, though having a theoretical discharge capacity of about 290 mAh/g, exhibits an initial discharge capacity as high as 285 mAh/g, which corresponds to a percent utilization of not less than 95%. Thus, it can be said that oxyhydroxide of nickel suffices for use requiring a high energy density battery such as power supply for note type personal computer.
However, oxyhydroxide of nickel is disadvantageous in that it doesn""t have a good cycle life. The improvement in cycle life is a great assignment to be accomplished for practical use. It has thus been desired to solve this problem.
As mentioned above, oxyhydroxide of nickel is expected as an effective candidate for positive active material for 3V nonaqueous electrolyte secondary battery. Oxyhydroxide of nickel exhibits a very high level of initial discharge capacity but is disadvantageous in that it doesn""t exhibit a good cycle life.
It is an object of the present invention to provide a nonaqueous secondary battery in which the cycle life is improved so that oxyhydroxide of nickel is practically used.
A nonaqueous-electrolyte battery according to the present invention comprises a positive active material containing oxyhydroxide of nickel and aluminum. In the nonaqueous-electrolyte battery according to the present invention, the positive active material may further contain oxyhydroxide of cobalt. Further, the nonaqueous-electrolyte battery according to the present invention may comprise an electrolyte containing heterocyclic compound containing nitrogen having lone pair as a constituent element of the heterocycle. The heterocyclic compound may be at least one selected from the group consisting of pyridine, pyrazine, pyridazine, pyrimidine, 1,3,5-triazine, 1,2,4,5-tetrazine, indolizine, quinoline, isoquinoline, cinnoline, 4H-quinolizine, quinazoline, quinoxaline, phthalazine, 1,8-naphthyridine, pteridine, acridine, phenazine, phenanthridine, 1,10-phenanthroline, benzo[c]cinnoline, 2,2xe2x80x2-piperidyl, benzo[g]quinoline, benzo[g]isoquinoline, benzo[h]quinoline, and benzo[f]quinoline.